FIG. 6 is a schematic diagram showing a conventional elevator apparatus similar to the one disclosed in Japanese Patent Application Laid-open No. Hei 2-110090.
As illustrated, in the elevator apparatus, a drive motor 2, a brake wheel 3 and a sheave 4 that constitute a hoisting machine are attached to a common rotational shaft 1. The motor 2 is electrically connected to a motor control circuit 5, and the motor control circuit 5 is connected through a contact 6 of an electromagnetic contactor to a three-phase power source 7.
An electromagnetic brake 8 is made up of a plunger 10 attached to a lining 9 that effects the brake by clamping the brake wheel 3, a spring 12 connected between the plunger 10 and a base 11, a switch 13 opened/closed in association with the motion of the plunger 10, and a brake coil 14 wound around the plunger 10.
In the electromagnetic brake 8, the plunger 10 is depressed by the force of the spring 12, that is, the lining 9 attached to the plunger 10 is pressed onto the brake wheel 3, thereby effecting the braking force. On the other hand, if the brake coil 14 is energized through a brake control circuit 15 that controls an electric current flowing in the brake coil 14, the plunger 10 overcomes the force of the spring 12, and is attracted, to thereby release the brake wheel 3.
A rope 16 is hung over the sheave 4, and one end of the rope 16 is connected to an elevator cage 17, whereas the other end thereof is connected to a counterweight 18.
FIG. 7 is a circuit diagram showing the conventional brake control circuits 15 shown in the block diagram of FIG. 6.
In a brake control circuit 15a shown in FIG. 7, between a positive terminal (+) of a DC power source (not shown) and a negative terminal (-) thereof, a contact 19 of the electromagnetic contactor (not shown) which is closed at the time of the release of the electromagnetic brake 8 and is open at the time of the operation of the electromagnetic brake 8, an electric current detector 22, the brake coil 14, and a semiconductor switch 20 are connected in series. Also, a flywheel diode 21 is connected in parallel with a serially connected assembly of the electric current detector 22 and the brake coil 14. Connected to the base of the semiconductor switch 20 is a voltage-drop control circuit 23 to which the output of the electric current detector 22 is inputted to ON/OFF control the semiconductor switch 20, i.e., to control the coil current through the pulse width control, thereby substantially dropping the voltage applied to the coil.
The brake control circuit 15a detects electric current flowing through the brake coil 14 by means of the electric current detector 22, and controls the brake current using a chopper system in which ON/OFF control is carried out by the semiconductor switch 20.
Also, in another brake control circuit , between a positive terminal (+) of a power source and a negative terminal (-) thereof, a contact similar to contact 19 shown in FIG. 7, a contact of the switch 13 shown in FIG. 6, and the brake coil 14 shown in FIG. 6 are connected in series. Further, a resistor 24 is connected in parallel with the contact 13a of the switch 13, and a resistor 25 is connected in parallel with the brake coil 14.
In this case, since a large electric current is required to flow through the brake coil 14 to overcome the force of the spring 12, so the plunger 10 is attracted, the contact 13a is in a closed state in which the brake coil 14 is directly connected to the power supply. However, it switches to an open state using such a characteristic that once the plunger 10 is attracted, the attracted state of the plunger 10 can be maintained even if the coil current is decreased.
Also, the resistor 24 connected in parallel to the contact 13a serves as a current limiting resistor that limits the current flowing the brake coil 14 when the plunger 10 is attracted and the contact 13a is open. The resistor 25 connected in parallel with the brake coil 14 serves as a coil protection resistor that absorbs the electromagnetic energy stored in the brake coil 14 when the coil current is interrupted. The brake current is controlled by the electromagnetic contactor 13a and the current limiting resistor.
In either of the above-mentioned types shown in FIG. 7 and described at the time of the brake attraction, the DC power source is directly connected to the brake coil 14 to cause a large current to flow therein. This generates a large energized magnetic force, thereby achieving the immediate brake release (pick-up). Once the brake is released, the voltage applied to both ends of the brake coil 14 is dropped by the action of the semiconductor switch 20 or the resistor 24 so as to limit the current flowing in the coil, thereby attracting and holding the brake. Consequently, it is possible to suppress the heat generation of the brake coil 14 as well as to reduce electric power consumption of the coil.
However, in the case where a only single system of the DC power source is provided as a control power source, and the power source cannot supply a required and sufficient high voltage for immediately releasing the electromagnetic brake, the conventional brake control circuit cannot release the brake immediately and, at worst, never releases the brake (plunger is not attracted), and therefore the elevator can not be driven.
In particular, since the recent tendency in elevators is also directed toward down-sizing and low electric-power consumption of the control apparatus, it is difficult to provide various control power sources using large-size commercially available transformers in accordance with needs as in a conventional fashion. Further, since the control voltage is made lower, the above-noted problem is unavoidable.
Further, the detailed description of the invention will be given below.
The control apparatus for an elevator is conventionally constructed of a large number of relays so as to be controlled by the relay-sequence. Therefore, the voltage used in the apparatus is relatively made high on assumption that the voltage enough to operate electromagnetic coils is to be supplied thereto. Further, since the hoisting machine is operated by the action of an electromagnetic coil, the brake of the hoisting machine has also been driven with the same voltage of the power source.
However, as the electronic technology for the control apparatus advances to replace the relay-sequence control with the computer control, its control voltage becomes low. Accordingly, if an electromagnetic coil for the low voltage is used, then the coil current at the time of attraction becomes relatively large, to thereby cause the voltage drop in a current supply line to the coil becomes large. Further, such a power source device as to have a large current capacity is required. In some cases, the attraction is liable to be difficult.
Furthermore, in the case where the voltage applied to the brake coil 14 is low, the flowing current is small and the attracting force is also low, thereby causing the motion slow and deteriorating the controllability. For this reason a separate power source remains to be provided for the brake coil. However, currently, since the most of the circuits are made electronic, it is required to eliminate the kinds of power sources.
The present invention has been made in view of the above, and therefore has an object of the present invention to provide a brake control apparatus for an elevator, which, in association with a tendency that the power source becomes lower in voltage, even if it is not provided with a power source having a high voltage that is necessary and sufficient at the time of the brake release, and even if it is provided with only one DC power source, can realize the brake release action by immediately supplying the necessary energy to the brake coil independently of the power source voltage at the time of the brake release.